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The tectonically active Taiwan orogen features numerous rivers that yield a high amount of sediment with fluxes exceeding 104 t/km2/yr. Amongst these, the landslide‐dominated Liwu River is well studied regarding its dynamic surface processes. However, the quantification of denudation in the Liwu Basin is still an ongoing task as rates obtained to date are subject to substantial differences depending on methods that differ in their spatio‐temporal scales. We constrain an upper limit of global denudation using the cosmogenic nuclide 10Be(meteoric) and its ratio to stable 9Be. Meteoric cosmogenic 10Be is delivered to Earth's surface by precipitation, whereas stable 9Be is released from rock weathering. In contrast to in situ cosmogenic 10Be measured in quartz, the 10Be(meteoric)/9Be ratio can be analyzed in quartz‐poor settings. 10Be(meteoric)/9Be‐derived denudation rates (Dmet) vary from 8.1 to >30 mm/yr in the Liwu mainstem, and from 3.4 to 21.5 mm/yr in the tributaries. These new Dmet are among the highest cosmogenic nuclide‐derived rates ever measured. Most of these rates agree with rates from sediment gauging or channel incision. We propose that stochastic landsliding plays a major role in denudation processes here. Using a soil‐bedrock mixing model and published riverine organic 14C data as a soil tracer, we estimate the fractional contribution of bedrock landslide material to mainstem sediments to be 55%–97%, which explains the magnitude and large variability (4‐fold) in Dmet. We demonstrate the complexity associated with denudation rates determination in landslide‐dominated routing systems; but also the potential of 10Be(meteoric)/9Be for tracing stochastic landsliding processes. Plain Language Summary: Many of Earth's rivers that transfer sediments with an extremely high rate are found in the Taiwan mountain belt, where earthquakes and typhoons are very common. Determination of the sediment removal rate in these rivers is crucial for understanding of the evolution of mountain landscapes through time and their impact on ocean chemistry and atmospheric trace gases. We applied a denudation rate meter to river sediments from one of the fastest‐eroding catchments in Taiwan, the Liwu River: the meteoric cosmogenic isotope beryllium‐10 (10Be) delivered by rainfall normalized to stable 9Be. This geochemical tool is particularly suited for fast‐eroding settings given the high delivery rate of meteoric 10Be to Earth's surface. The measured 10Be(meteoric)/9Be‐derived denudation rates in the Liwu Basin are highly variable and range from ∼3 to >30 mm/yr. We find that stochastic bedrock landsliding is likely the cause for such magnitude and large variability in denudation. Liwu river sediments constitute a mixture between steadily eroding surface soil and bedrock materials released from depths that lack meteoric 10Be. Our findings demonstrate the substantial potential of 10Be(meteoric)/9Be to trace sources of rainfall‐triggered landslides. Key Points: We apply the cosmogenic nuclide 10Be(meteoric) and its ratio to 9Be in one of the world's fastest‐eroding basin10Be(meteoric)/9Be ratios record extremely high denudation rates (>10 mm/yr)A soil‐bedrock mixing model reveals that bedrock landslides are the cause of the high denudation rates [ABSTRACT FROM AUTHOR]

The cosmogenic meteoric 10Be that is produced in the atmosphere and mainly scavenged by rainfall is a valuable tool for determining dates and rates of Earth surface processes. A key prerequisite for its applications is the knowledge of the long-term 10Be depositional flux to Earth's surface. Previous efforts on obtaining 10Be depositional fluxes include general atmospheric circulation modelling (GCM), empirical fitting of rainfall 10Be records, and determining the inventory of soil profiles of known age. Here, we derive 10Be depositional fluxes from Holocene river terrace 10Be inventories across the Taiwan mountain belt. We measured 10Be and 9Be concentrations from three terrace profiles, with 14C ages ranging between 3.83 and 9.05 cal. kyr BP and sampling depths of up to 6.2 m. Based on 10Be inventories of our river terraces, the calculated long-term 10Be depositional fluxes vary from 0.32 to 0.49 × 106 at/cm2/yr in the Taiwan orogen. We identify partial Be retention, surface erosion, multi-phase sediment deposition, and incomplete sampling depth in these terraces as potential causes of flux underestimation. When accounting for each of these factors and their uncertainties, the resulting flux estimates of each terrace show an overlapping range of 0.66–0.88 × 106 at/cm2/yr. This newly constrained flux range representative over millennial timescales is thus recommended for Earth surface applications in the fast-eroding Taiwan orogen, especially in regions with similar climatic conditions as the studied terraces. When comparing to flux estimates from other approaches, the flux from the rainfall-based fitting equation exceeds our new terrace-derived flux by more than a factor of two. We consider such high flux to be unlikely for the Taiwan orogen, and suggest that the control of precipitation on the 10Be flux here may be overestimated in rainfall data fitting. The GCM-derived flux overestimates the 10Be depositional flux in this setting to a smaller degree (at least 23%), which is in accordance with findings from previous global data compilation of 10Be fluxes. • We constrained Holocene 10Be depositional flux in Taiwan using 3 terrace profiles. • Measured terrace-derived flux is 0.32–0.49 × 106 at/cm2/yr. • These fluxes are similar to global flux models when considering flux uncertainties. • Such local calibration is essential to use meteoric 10Be in Earth surface studies. [ABSTRACT FROM AUTHOR]